Techniques for joining electrodes to one another with solder are known. Techniques in which solder having a relatively melting point, that is, low-melting-point solder, such as solder containing indium (In) or solder produced by adding silver (Ag) or the like to solder containing In is used for performing joining are known.
Low-melting-point solder is capable of being melted at a low temperature. However, if an internal structure (i.e., microstructure) having good mechanical properties is not formed when the low-melting-point solder melts and solidifies, it is difficult to form a solder joint having high durability to withstand external forces and stresses.
The followings are reference documents.                [Document 1] Japanese Laid-open Patent Publication No. 2013-233577, and        [Document 2] Japanese Laid-open Patent Publication No. 61-148774.        